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A europium metal-organic framework for dual Fe³⁺ ion and pH sensing.

ABSTRACT: Metal-organic frameworks (MOFs) with ratiometric sensing properties are desirable for many applications due to their intrinsic self-calibration. We report the re-assessment of the sensing properties of a MOF, originally reported as containing europium(III) and 2-hydroxyterephtalic acid, and having fluorescent ratiometric iron(III) sensing properties. Synchrotron single-crystal X-ray diffraction and proton nuclear magnetic resonance (¹H NMR) spectroscopy revealed that the MOF is composed of 2-methoxyterephthalate, not 2-hydroxyterephthalate as originally reported. We found that the MOF exhibits a sensor turn-off response towards Fe³⁺ ion concentrations in the range 0.5-3.7 ppm (band 425 nm), and a turn-on response towards a decrease of pH from 5.4 to 3.0 (band 375 nm), both resulting from the addition of acidic Fe³⁺ salt solution to a MOF suspension. Thus, the ratiometric sensing properties and the originally proposed mechanism no longer apply; our work reveals a dynamic quenching mechanism for the fluorescence turn-off response due to the presence of Fe³⁺ ions, and a ligand protonation mechanism for the turn-on response to a decrease in pH. Our work highlights the importance of a thorough investigation of the structure of any newly synthesized MOF, and, in the case of potential sensors, their selectivity and any environmental effects on their sensing behavior.

SUBMITTER: Rozenberga L

PROVIDER: S-EPMC9283444 | biostudies-literature | 2022 Jul

REPOSITORIES: biostudies-literature

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A europium metal-organic framework for dual Fe<sup>3+</sup> ion and pH sensing.

Rozenberga Linda L Skinner William W Lancaster David G DG Bloch Witold M WM Blencowe Anton A Krasowska M M Beattie David A DA

Scientific reports 20220714 1

Metal-organic frameworks (MOFs) with ratiometric sensing properties are desirable for many applications due to their intrinsic self-calibration. We report the re-assessment of the sensing properties of a MOF, originally reported as containing europium(III) and 2-hydroxyterephtalic acid, and having fluorescent ratiometric iron(III) sensing properties. Synchrotron single-crystal X-ray diffraction and proton nuclear magnetic resonance (<sup>1</sup>H NMR) spectroscopy revealed that the MOF is compos ...[more]

PMID: 35835797

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Project description:A versatile approach to modify metal-organic framework nanoparticles (NMOFs) with nucleic acid tethers, using the "click chemistry" method is introduced. The nucleic acid-functionalized NMOFs are used to prepare stimuli-responsive carriers of loads (fluorescence probes or anti-cancer drugs). Two different stimuli-responsive nucleic acid-based NMOFs are presented. One system involves the preparation of pH-responsive NMOFs. The NMOFs are loaded with fluorophores or doxorubicin anti-cancer drug and locked in the NMOFs by pH-responsive DNA duplex capping units. At pH = 5.0 the capping units are unlocked, leading to the release of the loads. The AS1411 aptamer is conjugated to the locking units as the targeting unit for the nucleolin biomarker present in cancer cells. The pH-responsive doxorubicin-loaded NMOFs and, in particular, the AS1411 aptamer-modified pH-responsive NMOFs reveal selective, targeted, cytotoxicity toward MDA-MB-231 breast cancer cells. A second system involves the synthesis of NMOFs that are loaded with fluorophores or doxorubicin and capped with metal-ion-dependent DNAzyme/substrate complexes as locking units (metal ion = Mg2+ or Pb2+ ions). In the presence of the respective metal ions, the nucleic acid locking units are cleaved off, resulting in the release of the loads. Also, "smart" Mg2+-ion-dependent DNAzyme capped doxorubicin-loaded NMOFs are synthesized via the integration of the ATP aptamer sequence in the loop domain of the Mg2+-dependent DNAzyme. The unlocking of these NMOFs proceeds effectively only in the presence of ATP and Mg2+ ions, acting as cooperative triggers. As ATP is over-expressed in cancer cells, the "smart" carrier provides sense-and-treat functions. The "smart" ATP/Mg2+-triggered doxorubicin-loaded NMOFs reveal selective cytotoxicity toward MDA-MB-231 cancer cells. Beyond the use of the metal-ion-dependent DNAzymes as ion-responsive locks of drug-loaded NMOF carriers, the DNAzyme-capped fluorophore-loaded NMOFs are successfully applied as functional units for multiplexed ion-sensing and for the design of logic-gate systems.

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A europium metal-organic framework for dual Fe³⁺ ion and pH sensing.

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A europium metal-organic framework for dual Fe<sup>3+</sup> ion and pH sensing.

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A europium metal-organic framework for dual Fe3+ ion and pH sensing.

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A europium metal-organic framework for dual Fe<sup>3+</sup> ion and pH sensing.

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OmicsDI is part of the ELIXIR infrastructure

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A europium metal-organic framework for dual Fe³⁺ ion and pH sensing.